[vlc-devel] Re: Multicast streaming over wifi

Rémi Denis-Courmont rdenis at simphalempin.com
Mon Nov 6 14:02:44 CET 2006

On Mon, Nov 06, 2006 at 04:50:17AM -0800, Greg Shepherd wrote :
> >most-likely-failed checksum will cause the packet to be discarded in the
> >IP stack, before being passed to the application.

> Sure you can, and it is done in many ways today. Some of the more
> effiecient FEC solutions today do not affect the original data stream.
> They simply create an additional stream of repair symbols to a
> different port.

That does ABSOLUTELY NOT address the UDP checksum problem. Both streams
(data and error correction) will have UDP checksumming, which by
definition prevents error correction. You need either a transport with
no payload checksum (and AFAIK, UDP-Lite is the only one on the
Internet), or you must do error correction below IP (which 802.11 does
by the way, though maybe not efficiently enough for multicast(?)).

Now, it certainly would be a good idea to add UDP-Lite to the official
VLC tree (and I plan on doing so), but I'd rather have it merged into
the official Linux kernel first, and if you want FEC on Windows or OSX,
I don't see any solution.

Rémi Denis-Courmont
looking for a job

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